Thursday, August 22, 2013

Thunderstorms possible Friday night/early Saturday as heat and humidity rise for the weekend..

Hot and humid weather will bereturning to southern MBthis weekend

After a couple of beautiful pleasant days with low humidity and mid 20 temperatures, things will be getting hotter and more humid over the weekend as a warm front pushes across southern MB. This front will usher in temperatures back in the thirties, along with noticeably more uncomfortable conditions as humidex values climb near the 40 mark over the weekend with increasing humidity levels. As the front pushes through Friday night, scattered thunderstorms will move across southern MB Friday night into early Saturday, with locally heavy rain, hail and intense lightning possible. Skies will clear out Saturday as the storms move out, leaving hot and humid conditions for the weekend with temperatures climbing into the 30-34C range across southern MB. Hot weather is expected to continue through much of the upcoming week, with temperature near or above the the 30C mark all week, along with the threat of scattered thunderstorms from time to time as weak impulses pass through southern MB. All in all, it looks like Mother Nature will be making up for some of our lost summer earlier this month. Stay cool!

26 comments:

Note that it's the dewpoint, not relative humidity, that will tell you how "uncomfortable" it is outside. Today we have dewpoints around 10C, which is very comfortable. The relative humidity is around 40% based on an air temperature of 24C.

Now, if the relative humidity was still 40% but the air temperature was 33C, the dewpoint would be around 18C. This would feel a lot more uncomfortable than 40% RH at 24C.

As a rough guide, here is a table of comfort levels relative to dewpoints..

Models are showing humidex values over 40 for Saturday for Winnipeg and RRV once early morning convection moves out. Temperatures of 32-34C with dewpoints of 20-21C will combine to produce humidex values of 40-43 Saturday afternoon/early evening.

Very challenging forecast for southern MB this weekend as we get into a hot, humid and unstable airmass with varying model opinions on extent, location and timing of any convective development (ie thunderstorms) that will be affecting our area. Due to the extreme volatility of this incoming airmass, there is the potential for locally severe thunderstorms that will produce very heavy rainfall, hail and damaging wind gusts.. with even the chance of tornadoes. That being said, the airmass will also be capped during the day, so things may not develop until evening hours, if at all. The first chance for thunderstorms is overnight tonight into early Saturday as storms blow up over SE SK and push into southern MB. GEM says most action will be through MB interlake, while NAM is further south through RRV including Winnipeg. RGEM is then showing some extremely heavy downpours Saturday night with thunderstorms (upwards of 100 mm with thunderstorms) while the NAM shows barely anything. Note that RGEM is also going crazy wit the dewpoints with values of 25C into RRV Saturday.. likely overdone, but would explain the extreme rainfall amounts the RGEM is showing. Such will be the case this weekend.. you may not see anything, but if you do, it could be big. Stay weather aware this weekend as things will be highly variable and changeable..

Big change in humidity levels coming up as dewpoints rise a good 5-10C over the RRV next within the next 24 hours. Currently, our dewpoints are in the comfortable 10-12C range in Winnipeg, but southerly winds are advecting much higher dewpoints in the 18-20C range over much of ND into western MB. Watch for our dewpoints to climb steadily this evening through tonight into Saturday, with values in the low 20s by Sat afternoon. Will be feeling much muggier by tomorrow morning!

"Partly cloudy. A few thunderstorms beginning early this evening and ending late this evening then 30 percent chance of showers late this evening and after midnight. Clearing before morning. Risk of a severe thunderstorm this evening. Risk of a thunderstorm late this evening and after midnight. Wind south 20 km/h gusting to 40 becoming light early this evening. Low 17."

I'm sorry to rant but this sucks! Wanted a storm so bad from this juicy air since this whole year has been dismal with so few storms. Sure we've had some good ones but just not enough. So why did we get missed this time? Why are they tracking where they are? It was so humid out today would've thought for sure we'd see something but of course we aren't.

Our storms this year (and for the last 2 for that matter) have been like an absentee father. You're always hopeful that you'll see them but then they don't show up. They can be related to the bombers as well!

Evan.. Totally agree with you. Such is the future of automated forecasts. Not only is that forecast horribly worded, it's not even right, which makes it even worse!

Thankfully, they amended the forecast to read..

"Tonight.. A few thunderstorms ending late this evening then partly cloudy with 30 percent chance of showers. Clearing before morning. Risk of a severe thunderstorm this evening. Wind south 20 km/h gusting to 40 becoming light early this evening. Low 17."

A lot simpler and easier to understand.

Unfortunately, we'll be seeing more of the original type of wording as worded forecasts become increasingly automated. One thing that becomes painfully obvious with automated forecasts.. the more details that are put in, the worse it sounds and the easier for the forecast to be wrong. If you truly want to automate the worded forecast, you have to keep it simple and concise.. "Tonight.. A few showers or thunderstorms this evening, some possibly severe, then clearing." Future programmers for weather services, please take note..

Hey Rob - Re The Public Weather Forecast.If I were The Minister, quite frankly I'd be more than a little embarrassed at the quality of the product EC is pumping out. It's an absolute disgrace that for modern country such as Canada, the public has to endure such low quality garbage. You can not plan any lengthy outside activity with this product. Speaking for myself, I don't trust EC's 12 hour look ahead let alone their 24 or 48 hour forecasts. They're an absolute joke and shud under no circumstances be used to plan anything involving detailed planning. Anyway, I know the future for humans at EC looks bleak with the possible exception for the managers who do all the cost cutting. Speaking for myself I have to wonder why radio and television regurgitate this product. I'd be using some other agency than EC even if I had to PAY for the product. Ya' get what ya' pay for and it's my feeling that EC will have zero customers in the future insofar as forecasts. Data acquisition - fine use AWOS all you want but for forecasts ... EC's "WATSON" needs a major overhaul or shud be scrapped.

EC has gone towards increased automation of the public forecast to concentrate more of their limited resources on "high impact weather" e.g. warnings of severe weather. This is where they feel a weather service is most vital, and I can't disagree with that. And in fact, EC is showing steady improvement in severe weather warning verification. However, I do feel that improvements can be made to computer generated public forecasts that we see and hear every day, even though they are not considered as high a priority as severe weather.

Honestly, I personally wouldn't even mind if EC put a couple advertisement boxes on their website.. as long as they aren't hugely disruptive. They need to find other sources of funds when the government is not feeling generous.

Looks like we'll be stuck with 30 degree weather for the rest of the week. Long range guidance is hinting at more seasonable weather moving in around Labour Day, but that's still a fair way's out to be more definite. Until then, try to take it easy out there. Hopefully, the heat isn't accompanied by humidity like we had yesterday with dewpoints in the 20s. That makes it especially tough to work outdoors..

Winnipeg has hit one record so far during this heat wave. The lowest temperature on August 24 was 21.2C, eclipsing the 21.1C temperature recorded in 1937 as the new daily high minimum temperature for the day.

We'll see if Winnipeg can keep the 30C streak alive tomorrow (2 days and counting). We have some high clouds moving in from the southwest tomorrow, which may cut down on the daytime heating depending on how extensive it is and keep us just shy of that 30C mark. If we hit it though, there's a chance we may be at the 30C mark all week.. which would be a significant streak, especially for this time of year.

>> Anonymous said...Rob, what does the thunderstorm potential look like this week? are we looking unstable weather this week or more stable and dry?

At this point, models aren't really showing much in the way of organized or enhanced thunderstorm activity over southern MB this week, despite the hot and fairly humid conditions. That's not to say we won't see any storms all week, as you can't rule out an occasional storm now and then with any weak impulses that are passing through, which the models don't really capture well. There's a huge upper ridge building to our south that will maintain very hot and dry weather south of the intl border. Here in southern MB, we'll be on the crest of that upper ridge, which is sometimes an area for tstorm development as impulses round the top of the ridge just north of the tstorm cap (so called "ridge rider" storms)

Overall though, looks generally hot much of the week with below normal precip for most areas. Will keep you posted if there's any changes to that thinking this week..

Winnipeg hit its second record daily high minimum temperature in a row. The new high minimum for August 25 is 19.7C, up 0.3C from the previous record. Also, for August 24, the new record was even greater than previously mentioned. It was 21.4C; not 21.2C.

Another 30c+ day in Winnipeg today as that cirrus layer has been pretty thin over us, alowing good surface heating this afternoon. That's our third 30C day in a row here and it looks like we may be at 30C plus much of the week. Tomorrow we have slightly cooler air coming in as a weak trough comes through overnight.. but we should have enough sun to get us close to 30C mark again in the afternoon. After that, 30C+ looks likely Wed into Sat, barring any thunderstorms/debris cloud that could jeapordize a 30C reading during any of those days.

Another strange public forecast out of Winnipeg. Calling for Norway House and Island Lake to get 5-10 mm through the day tomorrow, yet the GEM, NAM, GFS, SCRIBE, and EURO all have either no rain and clearing skies, or possibly 0.5mm and some cloud.